1. Field of the Invention
This invention relates to a multiroom air conditioner or heat-pump type air conditioner for blowing out heat-exchanged air.
2. Description of Related Art
In the air conditioner, there has been known a multiroom air conditioner in which plural indoor units each having an indoor heat-exchanger and an electric expansion valve are linked in parallel to a single outdoor unit having a compressor and an outdoor heat-exchanger. This type of air conditioner is disclosed in U.S. Pat. No. 5,222,371, for example.
In this type of air conditioner, condensed liquid refrigerant is frequently trapped in an indoor heat exchanger when an electric expansion valve is completely closed at the stop time of a room heating operation or the like. Therefore, the air conditioner falls into a gas-lacking state, and thus reduction in capacity is unavoidable. In order to avoid this problem, even when the room heating operation is ceased, the electric expansion valve is kept opened with smaller opening degree than that during the room heating operation, thereby preventing the trap of the refrigerant in the indoor heat-exchanger when the room heating operation is ceased.
As described above, the electric expansion valve is kept somewhat opened, so that the sound of refrigerant occurs in the expansion valve to induce noise. Particularly with respect to the electric expansion valve, the valve opening degree of the electric expansion valve is controlled by an electric motor (pulse motor), and thus there is a fact that it is difficult to accurately set the valve opening degree to a desired value due to a rotation error of the motor, etc. In addition, there is another fact that gas-liquid mixed refrigerant flows through the expansion value during the room heating operation and during the stop of the room heating operation. The sound (noise) of the refrigerant as described above is extremely magnified by a multiplied effect of these facts.